(1) Intensity Feedback of a Slowly Extracted Ion Beam at the HIT Synchrotron
[C. Schömers, HIT, Heidelberg, Germany]
Since November 2009 more than 2000 tumour patients have been treated at the Heidelberg Ion Therapy-Centre (HIT). The HIT synchrotron produces a library of energy, focus and intensity-variable pencil beams used to deliver dose distributions of utmost conformity to irregularly shaped target volumes. The required number of particles for each volume element of the tumour, which can vary by more than two magnitudes, is applied using the raster scan technology. The irradiation-time and thus the patient throughput are highly sensitive to the achieved spill-structure driven by RF-Knockout extraction. Presently unfavorable fluctuations of the extracted intensity due to inhomogeneous phase space distribution of the beam are present. Recently a feedback-loop coupling the dose- defining ionization chamber in front of the patient with the RF-Exciter was implemented allowing for the adaptation of the extracted intensity to the patient-specific treatment plan in real-time. The technical implementation and the impact on the clinical operation will be discussed.
(2) Magnetic Field Control (B-Train) Using a High Precision Integrator to Optimize the Duty Cycle of the HIT Synchrotron
[E. Feldmeier, HIT, Heidelberg, Germany]
For the Magnetic Field Control of the synchrotron at the Heidelberg Ion Therapy Centre the magnetic fields are measured with a pickup coil along the beam pipe. The induced pickup voltage, corresponding to changes in the magnetic field, has to be integrated in real-time to determine the actual field. A high precision integrator has been developed to measure fields with an accuracy of 4ppm over 10 seconds. This new integrator has a very low drift and calibrates during the measurement. Since December 2011 HIT started to use the magnetic field feedback control for its clinical operation. Therewith the magnetic field deviation of the dipole magnets in the synchrotron depending on eddy currents and hysteresis are no longer in effect. Waiting times on the flattop of the synchrotron cycle are no longer necessary and the efficiency of the accelerator is increased significantly.
ATS Seminars Organisers: H. Burkhardt (BE), M. Modena (TE), T. Stora (EN)
Coffee / tea will be served after the seminar
